U.S. patent number 6,740,042 [Application Number 10/236,067] was granted by the patent office on 2004-05-25 for bilateral simultaneous doppler measurement of segmented sphygmomanometry.
This patent grant is currently assigned to Biomedix, Inc.. Invention is credited to David A. Lerner, William Lee Rogers.
United States Patent |
6,740,042 |
Lerner , et al. |
May 25, 2004 |
Bilateral simultaneous doppler measurement of segmented
sphygmomanometry
Abstract
A system and method for simultaneous, bilateral, segmental blood
pressure measurement are disclosed. In one illustrative embodiment
of the invention, two Doppler modules are configured to operate at
nominally the same Doppler carrier frequency so that they probe for
substantially the same range of physiological information. However,
the Doppler carrier frequencies for the Doppler modules are also
sufficiently different to substantially avoid interference between
the two modules. A phase-locked loop (PLL) used to demodulate the
velocity signals in each Doppler module efficiently blocks
interference signals because they have frequencies that are the
difference in the Doppler carrier frequencies and that are outside
the locking range of the PLL. Broad-band RF amplifiers and Doppler
transducers are used to ensure that the frequency responses of the
Doppler modules are substantially the same.
Inventors: |
Lerner; David A. (St. Paul,
MN), Rogers; William Lee (Oakdale, MN) |
Assignee: |
Biomedix, Inc. (Vadnais
Heights, MN)
|
Family
ID: |
32314336 |
Appl.
No.: |
10/236,067 |
Filed: |
September 5, 2002 |
Current U.S.
Class: |
600/453 |
Current CPC
Class: |
A61B
8/04 (20130101); A61B 8/06 (20130101) |
Current International
Class: |
A61B
8/04 (20060101); A61B 8/06 (20060101); A61B
008/06 () |
Field of
Search: |
;600/407,437,438,440,441,442,443,446,447,448,449,450-471,485,487,490,492,493,497,500,504,508-520 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Imam; Ali
Attorney, Agent or Firm: Faegre & Benson LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
The present application claims priority to U.S. Provisional
Application No. 60/317,282, entitled "BILATERAL SIMULTANEOUS
DOPPLER MEASUREMENT OF SEGMENTED SPHYGMOMANOMETRY" and filed Sep.
5, 2001. Said Provisional Application is incorporated herein by
reference.
Claims
What is claimed is:
1. A system for simultaneously measuring blood pressures at least
two locations on a body, the system comprising: (a) a first Doppler
module tuned to a first Doppler carrier frequency and configured to
obtain a first signal from one of the two locations, the first
signal being indicative of a parameter of blood flow at the first
location; and (b) a second Doppler module tuned to a second Doppler
carrier frequency, which is higher than the first Doppler carrier
frequency by at least about 25 kHz and configured to obtain a
second signal from the other one of the two locations, the second
signal being indicative of a parameter of blood flow at the second
location, the two Doppler modules being configured to obtain the
respective signals substantially simultaneously.
2. The system of claim 1, wherein the second Doppler carrier
frequency is further higher than the first Doppler carrier
frequency by at least about 100 kHz.
3. The system of claim 1, wherein each Doppler module has a Doppler
velocity signal output port with an output bandwidth, and the
second Doppler carrier frequency is higher than the first Doppler
carrier frequency by an amount greater than the output
bandwidth.
4. The system of claim 3, wherein each Doppler module further
includes a phase-locked loop operatively connected to the output
port and configured to transmit the Doppler velocity signal to the
output port, the phase-locked loop having a lock range, wherein the
difference between the second and first Doppler carrier frequencies
is greater than the lock range.
5. The system of claim 3, wherein each Doppler module further
includes a Doppler transducer configured to receive ultrasonic
signals from a body and convert the signals into radio-frequency
electrical signals, and a radio-frequency amplifier operatively
connected to the transducer.
6. The system of claim 5, wherein the transducer in each Doppler
module has a bandwidth of about 3 MHz.
7. The system of claim 5, wherein the transducer in each Doppler
module has a bandwidth of about 4 MHz.
8. The system of claim 5, wherein each Doppler module further
includes a transducer housing having a patient-contacting end
configured to contact a patient's skin over an area, the transducer
being oriented within the transducer housing such that when the
patient-contact area of the housing is placed in contact with a
patient's skin over an area, the transducer is inclined with
respect to the skin area at an angle between about 40 to about 60
degrees.
9. The system of claim 8, wherein the transducer housing defines a
height that is smaller than a dimension of the patient-contact
area.
10. The system of claim 5, wherein the amplifier has a passband
having a bandwidth of at least about 1 MHz.
11. The system of claim 5, wherein the amplifier has passband
having an adjustable center frequency.
12. The system of claim 10, wherein the amplifier is tuned to at
least a first frequency for measuring blood pressure of deep
vessels and a second frequency for measuring blood pressure of
shallow vessels.
13. The system of claim 5, wherein each Doppler module further
includes an audio output configured to transmit signal indicative
of the frequency difference between a signal launched into the body
and a signal received from the body in response.
14. A system for simultaneously measuring blood pressures at least
two locations on a body, the system comprising: (a) a first Doppler
module tuned to a first Doppler carrier frequency and configured to
obtain a first signal from one of the two locations, the first
signal being indicative of a parameter of blood flow at the first
location; and (b) a second Doppler module tuned to a second Doppler
carrier frequency, which is higher than the first Doppler carrier
frequency by at least the greater of the maximum frequency of human
hearing and a maximum Doppler frequency expected due to hemodynamic
flow, and configured to obtain a second signal from the other one
of the two locations, the second signal being indicative of a
parameter of blood flow at the second location, the two Doppler
modules being configured to obtain the respective signals
substantially simultaneously.
15. The system of claim 14, wherein each Doppler module further
includes a demodulator having a bandwidth and configured to
generate a signal indicative of the speed of the blood flow, and
the second Doppler carrier frequency is higher than the first
Doppler carrier frequency by at least the greatest of (a) the
maximum frequency of human hearing, (b) a maximum Doppler frequency
expected due to hemodynamic flow and (c) a bandwidth of the
demodulator.
16. The system of claim 15, wherein the demodulator includes a
phase-locked loop having a lock range, the second Doppler carrier
frequency is higher than the first Doppler carrier frequency by at
least the greatest of (a) the maximum frequency of human hearing,
(b) a maximum Doppler frequency expected due to hemodynamic flow
and (c) the lock range of the phase-locked loop.
17. A method of measuring blood pressure in a body, the method
comprising: (a) launching a first ultrasonic signal of a first
Doppler carrier frequency into a first location of the body; (b)
receiving a first response signal from the first location, the
first response signal being indicative of a parameter of blood flow
at the first location; (c) substantially simultaneously with step
(a), launching a second ultrasonic signal of a second Doppler
carrier frequency into a second location of the body, the second
Doppler carrier frequency being higher than the first Doppler
carrier frequency by at least about 25 kHz; and (d) receiving a
second response signal from the second location, the second signal
being indicative of a parameter of blood flow at the second
location.
18. The method of claim 17, further comprising comparing the first
and second response signals.
19. The method of claim 17, further comprising: (e) applying a
sufficient first pressure at the first location to stop blood flow
in a blood vessel in the first location; (f) applying a sufficient
second pressure at the second location to stop blood flow in a
blood vessel in the second location; (g) after steps (e) and (f),
reducing while monitoring the first and second pressures until the
blood flows in both blood vessels are restored; and (h) repeating
steps (a) through (d) throughout step (g); and (i) determining,
from the signals received in steps (b) and (d), the levels of the
first and second pressures at which the blood flows in the blood
vessels in the first and second locations, respectively, are
restored.
20. The method of claim 17, further comprising: (e) generating a
first output signal derived from the first ultrasonic signal and
the first respond signal; and (f) generating a second output signal
derived from the second ultrasonic signal and the second respond
signal.
21. The method of claim 20, wherein the parameter of blood flow at
each location is the speed of blood flow at that location, and each
output signal is an audio signal having a frequency proportional to
the speed of blood flow at the respective location.
22. The method of claim 20, wherein the parameter of blood flow at
each location is the speed of blood flow at that location, and each
output signal has amplitude proportional to the speed of blood flow
at the respective location.
23. The method of claim 17, wherein the second Doppler carrier
frequency is higher than the first Doppler carrier frequency by at
least the greater of the maximum frequency of human hearing and a
maximum Doppler frequency expected due to hemodynamic flow.
24. The method of claim 23, wherein the step of receiving a first
response signal includes demodulating the first response signal
using a first demodulator, and the step of receiving a second
response signal includes demodulating the second response signal
using a second demodulator, each of the modulators having a
bandwidth, and the second Doppler carrier frequency is higher than
the first Doppler carrier frequency by at least the greatest of (a)
the maximum frequency of human hearing, (b) a maximum Doppler
frequency expected due to hemodynamic flow and (c) a bandwidth of
the demodulator.
Description
FIELD OF THE INVENTION
The invention relates generally to blood pressure measurement. More
particularly, the invention relates to a method and system for
simultaneous, bilateral, segmental measurement of blood pressure
using Doppler techniques.
BACKGROUND OF THE INVENTION
Segmental blood pressure is one of the most important parameters to
measure in understanding and diagnosing vascular diseases. Blood
pressure measurement (sphygmomanometry) for segmental systolic
pressures using Doppler techniques has gained wide acceptance, and
is the modality of choice in many incidences. This is in large part
because of Doppler's greater sensitivity and accuracy when compared
with photoplethysmographic and oscillometric methods and the
Doppler method's lesser sensitivity to temperature fluctuations.
The Doppler-based systems also have the desirable characteristic of
being vessel-specific.
One application of Doppler sphygmomanometry is in segmental blood
pressure measurements, i.e., tracking blood pressures at different
parts of the body. For example, because of its vessel-specificity,
Doppler sphygmomanometry can be used to trace blood pressures along
an artery in limbs for diagnosis of peripheral arterial disease
(PAD).
In performing segmented blood pressure measurements, it is often
desirable to conduct bilateral measurements, i.e., measurements at
symmetrically paired locations, such as left and right feet, and
left and right forearms. The comparison between blood pressures at
symmetrical locations may yield clues to the condition of blood
vessels on either side. The ideal time for making such comparisons
would be when the blood pressures at both locations are measured
for the same heartbeat so that any differences between the
measurements are not attributable to the difference in the
different heartbeats.
However, simultaneous bilateral Doppler measurements have not been
successfully used in conventional systems and techniques. One
conventional approach is to employ two separate Doppler circuits
operating at nominally the same frequency, e.g., 8 MHz. Such
approach suffers from at least two drawbacks. First, it is
difficult to maintain an exact frequency match between the two
circuits; second, as schematically illustrated in FIG. 9, even if
the drivers 910, 920 of the two Doppler circuits could be matched
exactly, or even if the two drivers were in fact a common driver,
the signals in both circuits are like to cross-couple (930) with
each other, both electronically and acoustically due to the
nearly-identical frequencies of the signals. The magnitude of the
error signals resulting from such interference is in the same
bandwidth, and can be on the same order of magnitude or even
greater than, the useful signals. Driving two transducers from a
common signal driver to eliminate frequency drift does not solve
the cross coupling problem as the return Doppler signals can cross
couple in the same way as heretofore described.
The invention disclosed herein is aimed at providing a system and
method for simultaneous, bilateral measurement of segmental blood
pressures substantially without the drawbacks of the conventional
approaches.
SUMMARY OF THE INVENTION
Generally, the invention provides a system and method whereby two
Doppler measurements of blood flow at two different locations on a
body are carried out substantially simultaneously, i.e., within the
same heartbeat with minimum interference from each other.
In one illustrative embodiment of the invention, two Doppler
modules are configured to operate at nominally the same Doppler
carrier frequency so that they probe for substantially the same
range of physiological information. However, the Doppler carrier
frequencies for the Doppler modules are also sufficiently different
to substantially avoid interference between the two modules. A
phase-locked loop (PLL) used to demodulate the velocity signals in
each Doppler module efficiently blocks interference signals because
they have frequencies that are the difference in the Doppler
carrier frequencies and that are outside the locking range of the
PLL. Broad-band RF amplifiers and Doppler transducers are used to
ensure that the frequency responses of the Doppler modules are
substantially the same.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the invention will become apparent
upon reading the following detailed description and upon reference
to the drawings in which:
FIG. 1 schematically shows an over-all system for simultaneous
segmental sphygmomanometry in one embodiment of the invention;
FIG. 2(a) schematically shows a double-tuned RF amplifier used in a
Doppler module in an embodiment of the invention;
FIG. 2(b) schematically shows the frequency response
characteristics of the amplifier shown in FIG. 2(a);
FIG. 3 schematically shows various aspects of a Doppler transducer
module in an embodiment of the invention;
FIG. 4 shows in block-diagram form the structure of a Doppler
Module in an embodiment of the invention;
FIG. 5 schematically shows the forms of a Doppler velocity signal
and Demodulated Doppler audio signal output from a Doppler module
in an embodiment of the invention;
FIG. 6 schematically shows an arrangement for simultaneous
segmental sphygmomanometry in one embodiment of the invention;
FIG. 7 schematically shows a sample result of simultaneous
segmental sphygmomanometry accompanied by the result of PVR
measurements in one embodiment of the invention;
FIG. 8 schematically shows a phase-locked loop used in a Doppler
module in an embodiment of the invention; and
FIG. 9 schematically shows a convention arrangement for
simultaneous blood flow measurement.
While the invention is susceptible to various modifications and
alternative forms, specific embodiments thereof have been shown by
way of example in the drawings and are herein described in detail.
It should be understood, however, that the description herein of
specific embodiments is not intended to limit the invention to the
particular forms disclosed, but on the contrary, the intention is
to cover all modifications, equivalents, and alternatives falling
within the spirit and scope of the invention as defined by the
appended claims.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
Generally according to the invention, a system and method for
simultaneous (i.e., within the same heartbeat) blood flow
measurements at two or more locations on a patient's body are
provided. The system in one embodiment includes one Doppler module
for taking measurements from each location. All Doppler modules are
tuned to nominally the same frequency (e.g., 8 MHz) but each is
tuned to a slightly different Doppler carrier frequency (e.g., 7.8
MHz) from the others. The difference is sufficiently large so that
the interference between the modules is sufficiently small in the
output frequency range of interest.
An over-all system 100 embodying the invention is schematically
illustrated in FIG. 1. Two Doppler modules are used. The left
Doppler module 110 is configured to launch ultrasonic signals into
one side of a patient's body and generate from the ultrasonic
signals received back from the body two signals: (1) a left Doppler
velocity signal, V.sub.L (t), which is indicative of the speed of
blood flow; and (2) a left Doppler audio signal, S.sub.L (t), the
frequency of which is the difference in frequency between the
ultrasonic signal launched into the patient and the response signal
received by the module 110. The right Doppler module 120 is
identically constructed as the left Doppler module 110 but is
intended to be place on the other side of the patient's body to
generate a right Doppler velocity signal, V.sub.R (t) and a right
Doppler audio signal, S.sub.R (t). Although velocity and audio
signals are used in this illustrative embodiment to enhance the
reliability and ease of use of the system, it is not necessary to
have both types of signals. However, typically audio signals are
used at least to aid the location of blood vessels. The two modules
110, 120 are tuned to different Doppler carrier frequencies, as
described in more detailed below.
The Doppler modules 110 and 120 are tuned nominally at the same
carrier frequencies. For example, for shallow vessel studies, the
modules can be tuned to around 8 MHz. However, they are
deliberately tuned to carrier frequencies that differ from each
other by an amount that results in minimized interference in the
desired signals produced by the modules 110, 120. The carrier
frequency difference is typically at least the greatest of (a) the
maximum frequency of human hearing, if audio signals are used, (b)
the maximum Doppler difference frequency expected to be found due
to hemodynamic flow, and (c) the bandwidth of the demodulator (such
as the lock range of the PLL; see below) in the Doppler module.
Thus, for example, for a maximum human hearing range of 25 kHz,
maximum expected Doppler shift of 15 kHz and PLL lock range of 10
kHz, the carrier frequency difference should typically be at least
25 kHz. A safer choice would be to have a carrier frequency
difference of at least the sum of the three factors above. For the
above numerical example, the difference would be about 50 kHz.
Further enhancement of signal quality can be achieved by choosing
an even greater frequency difference, such as 100 kHz or 200
kHz.
For example, one of the modules can be tuned to 8 MHz and the other
8.2 MHz. For the same blood flow conditions, the two modules do not
produce perceptibly different Doppler audio or velocity signals.
But the 200 kHz frequency difference ensures that any interference
between the two modules will have a frequency of 200 kHz, which is
sufficiently distant from all frequencies of the desired signals
and thus easily filtered. The 200 kHz frequency is also outside the
lock range of the phase-locked loop 492 (see below) and audio
range. The interference noise is therefore minimized.
The signals produced by the Doppler modules 110, 120 are sent to a
Multiplexing analog-to-digital (A/D) converter 130 to be digitized
for later computer processing. The precise method and order of
multiplexing and conversion is not critical to the invention. Any
number of alternative devices and methods can be used in place of
the converter 130. For example, the signals need not be
multiplexed, but instead sent in parallel for subsequent computer
processing. A computer interface (140), such as a digital I/O board
receives the digitized signals and transfer them to a computer 150,
which in the illustrative embodiment is a personal computer (PC)
but can be any suitable computer or processor. The computer 150 is
programmed to perform from the basic functions such as calculating
and displaying blood pressures from the various signals to
automating signal detection, as described later.
Each of the Doppler modules 110, 120, as schematically shown in
FIG. 4 (labeled 400) includes a probe or transducer module 210,
which is driven by an oscillator driver 420, the frequency of which
is in turn controlled by a frequency selector 410. The transducer
module 210 can launch ultrasonic signals into a patient body and
receive echoes back. The echoes, which are ultrasonic signals, are
converted into radio-frequency (RF) signals by the transducer
module 210, which then sends the RF signals to an RF amplifier 220.
The amplifier 220 can be any suitable amplifier for the signals,
but in the illustrative embodiment of the invention is a
"double-tuned" RF amplifier, as schematically shown in FIG. 2(a).
Signals from the transducer module 210 is fed to the amplifier 220,
which includes an RF transistor 240 and two inductor-capacitor
pairs L.sub.1 (222)-C.sub.1 (224) and L.sub.2 (226)-C.sub.2 (228).
Each pair results in a resonance frequency in the amplifier's
frequency response. Thus the amplifier is tuned to two frequencies
(channels) by adjusting the values of the appropriate inductors or
capacitors. In the illustrative embodiment, the amplifier is tuned
to 8 MHz and 5 MHz, respectively. The former Doppler frequency is
better suited for studying shallow vessels while the latter more
suited for deep vessels. Again, the bandwidth of each channel is
narrow enough to reject unwanted interference but large enough
(e.g., about 200 kHz) to be suitable for a range of Doppler carrier
frequencies
The transducers module 210 used are wide-band ultrasonic
transducers to ensure that the frequency response is substantially
the same no matter what carrier frequency a Doppler module is tuned
to with in the specified range. For example, the bandwidth in an
illustrative embodiment is chosen to be large enough to encompass
the carrier frequencies for both shallow and deep vessels and the
range of possible frequency settings for each nominal frequency, as
discussed above. Thus, for the example above of the RF amplifier
tuned to 8 and 5 MHz, the transducers have bandwidths of about 3
MHz or larger, for example 4 MHz.
The transducer modules can also be physically configured for
convenient application and minimizing motion artifact. In one
embodiment of the invention, as shown in FIGS. 3(a) and 3(b), a
transducer module 300 includes leads 320, housing 340 and
transducer 330 connected to the leads and situated within the
housing. The transducer 330 is typically positioned inside the
housing 340 in such a way that when the housing is attached to a
patient in the intended manner, the transducer is oriented with a
component of the orientation vector parallel to the blood flow in
the target blood vessel. The housing 340 is a slanted section of a
circular cylinder, with the plane defined by a patient-contacting
end 310 not being perpendicular to the longitudinal axis of the
cylinder. The transducer 330, in contrast, is positioned
perpendicular to the longitudinal axis of the cylinder. Thus, when
the transducer module 300 is properly positioned on a patient with
the patient-contacting end in contact with a portion of the
patient's skin, the transducer is at an angle from, and not
parallel or perpendicular to the portion of the skin. For example,
an angle of 40 to 60 degrees. A similar arrangement is show in
FIGS. 3(c) and 3(d), where the housing 340 is shown as a right
circular cylinder but with the transducer 330 positioned at an
angle from the longitudinal axis of the cylinder.
In both examples, the transducer modules are "flat", i.e., the
height of the modules 330 (the dimension perpendicular to the
patient-contacting end) is smaller or at least not substantially
larger than the dimensions of the patient-contacting end. This
configuration allows the transducer modules to be easily and
securely fastened to a patient, as shown in FIG. 6. Motion
artifacts are therefore greatly reduced.
Referring again to FIG. 4, the amplified RF signal from the
transducer module 210 is mixed by mixer 470 with the original
signal from the oscillator driver 420 through a phase shifter 430
but without any phase shift. The result of the mixing is an audio
signal S(t), with a frequency of the difference between the inputs
to the mixer 470. The amplified signal is also mixed by mixer 450
with a 90-degree-shifted oscillator driver signal. The resultant
signal is mixed by mixer 460 with a signal generated by a
quadrature pilot oscillator 440, which is an oscillator having two
outputs that are of the same frequency but shifted 90.degree. from
each other. The frequency of the oscillator 440 can be chosen at
any value that is at least the maximum Doppler shift in magnitude
away from the baseband. For blood pressure measurements, it is
typically at least 100 kHz and well away from the Doppler carrier
frequencies. The audio signal S(t) is mixed by mixer 480 with a
90-degree-shifted signal generated by the quadrature pilot
oscillator 440. The outputs of mixers 460 and 480 are combined by a
summer 490 to produce an intermediate-frequency signal, which is in
turn demodulated by a phase-locked loop (PLL) 492 to produce a
Doppler velocity signal, V(t), which has an amplitude that is
proportional to the speed of the detected blood flow, as shown in
FIG. 5 (404).
The PLL, an example of which is shown in FIG. 8, is a device well
known in the art and provides several advantages over other
alternative devices and methods for demodulation. First, it allows
for small amplitude frequency components to contribute to the time
domain output. Second, it can selectively sense small signals over
noise. Third, it generally rejects small amplitude, out-of-band
signals that might typically trigger other types of demodulators,
such as a zero crossing detector. Fourth, it rejects signals with
frequencies beyond the lock range, thus ensuring that a Doppler
module does not interfere with another Doppler module on the
contra-lateral side.
A further illustrative embodiment of the invention is schematically
shown in FIG. 6. Pairs of inflatable cuffs 610 are wrapped around a
patient (600)'s respective legs and feet. Each cuff 610 is equipped
with a calibrated pressure sensor (not shown) for measuring the air
pressure in the cuff 610). A disk-shaped Doppler sensor 300 is
secured against the patient's skin and oriented to measure blood
pressures from a set of predetermined arteries. A pen-style Doppler
transducer 620 is readily accessible to the physician or
technologist 660 carrying out the measurements. Each transducer
300, 620 is attached to its corresponding Doppler module.
Alternatively, the pairs of transducers 300 at different segments
(feet, ankles, calves, etc.) are connected time-wise sequentially
to the same pair of Doppler modules through a set of switches,
which can be manually or electronically operated. The Doppler
modules 300, 620 can be controlled by a computer, such as a PC 630,
which also includes a display 640 for monitoring (650) the
measurements. The inflation and deflation of the cuffs and cuff
pressure monitoring can also be computer controlled.
In operation, each pair of Doppler modules 300 operate at slightly
different frequencies from each other as described above. For
measurements in each section, the corresponding cuffs 610 securing
the transducers 300 in the section are first inflated until the
blood flow through the arteries in the section is stopped. At this
point, because there is no blood speed in the section, both the
Doppler velocity signal and Doppler audio signal are zero. As the
cuff pressure is gradually decreased, at some cuff pressure, blood
flow resumes, and Doppler audio and velocity signals are again
detected, as schematically shown in FIG. 5. The cuff pressure
measured at the onset of resumption of the Doppler signals is the
systolic blood pressure. If the blood flow resumes sooner on one
side than it does on the other, the patient has different segmental
blood pressure on different sides. Drastically asymmetrical
segmental blood pressures, as in the example shown in FIG. 7
(740-790), may indicate vascular ailment. The segmental pressure
results can further be compared with results from using other
techniques, such as pulse volume recording (PVR) for the same
regions to gain further insight, as shown in FIG. 7, which shows
markedly blunted PVR wave forms for the right leg in the same
regions where the Doppler segmental pressures are asymmetrical.
According to another aspect of the invention, the computer 150,
which in an illustrative embodiment is a PC, can be programmed to
increase the efficiency and reliability of blood pressure
measurements. For example, an algorithm is utilized to enhance
signal discrimination in the following illustrative way.
Both the Doppler audio signals and Doppler velocity signals are
sampled during the cuff inflation and deflation processes and
temporarily stored in memory. The computer 150 continuously
examines the signals to see if a particular threshold amplitude for
each type of signals is exceeded. If both types of signals have
exceeded their respective thresholds a set number of (e.g., three)
consecutive times in the same time frame, then the first detected
signals that exceeded their respective thresholds are deemed
valid.
As another example, the PC 150 can be programmed to automatically
determine if a signal has reached a threshold level. For example, a
threshold level can be set at a predetermined gradation (e.g.,
first gradation) on the graphic display 640. Increasing the gain of
displayed signal ("zooming in") therefore has the effect of
lowering the threshold, and decreasing the gain has the opposite
effect. Thus, a user can adjust the threshold to a level most
suitable for his or her particular application.
Thus, the invention enables simultaneous, bilateral segmental blood
pressure measurement using the ultrasonic Doppler method, which is
the method of choice for studying vascular diseases. Unlike other
techniques, the invention provides both waveforms as output
(velocity signals) as well as audio signals. Photoplethymography,
for example, only provides waveforms outputs. In addition,
simultaneous bilateral testing significantly reduces testing time
while maintaining, or enhancing the quality of testing.
The particular embodiments disclosed above are illustrative only,
as the invention may be modified and practiced in different but
equivalent manners apparent to those skilled in the art having the
benefit of the teachings herein. Furthermore, no limitations are
intended to the details of construction or design herein shown,
other than as described in the claims below. It is therefore
evident that the particular embodiments disclosed above may be
altered or modified and all such variations are considered within
the scope and spirit of the invention. Accordingly, the protection
sought herein is as set forth in the claims below.
* * * * *